1. Field of the Invention
The present invention relates to metallurgies for contacting silicon semiconductors to form ohmic and Schottky barrier diode contacts.
2. Description of the Prior Art
The requirements for a material or combination of materials to provide ohmic and Schottky barrier contacts to semiconductor substrates are very stringent from both an electrical and chemical standpoint.
Numerous metallurgical systems which are known to semiconductor designers have been proposed and utilized as ohmic and Schottky barrier diode contacts. The single most successful metal used in interconnections of silicon planar transistors and integrated circuits is aluminum or aluminum which is doped with a small amount of copper. Aluminum makes good ohmic and mechanical contact to the silicon and to the surrounding insulation layers. It is easy to deposit by standard evaporation or sputtering techniques and can be easily patterned by etching or similar techniques. However, aluminum has a tendency to interact with silicon, particularly during high temperature processing. In addition, aluminum alone forms neither a very high-nor a low-barrier height Schottky barrier contact to silicon.
The literature is replete with various other metallurgical systems which fulfill one or more functions as metallurgical contacts. One of the most successful of these systems is a titanium-tungsten alloy which has achieved widespread use in the industry as a barrier layer between aluminum and silicon. However, titanium-tungsten cannot be evaporated onto a semiconductor substrate; it must be sputtered. Thus, this alloy cannot be patterned using a lift-off process.
For quite some time a need has existed for a Schottky barrier diode with a low barrier height, i.e., around 0.5 electron volts. For example, in a diode transistor logic (DTL) circuit, it is desirable that the barrier height of the input diodes be around 0.5 electron volts. In particular, the DTL type circuit commonly referred to as C.sup.3 L is most useful when the Schottky diodes, which perform the input AND function in the circuit, exhibit said barrier height. The C.sup.3 L circuit is described in the publication by A. W. Peltier entitled "Advances in Solid-State Logic--A New Approach to Bipolar LSI: C.sup.3 L", 1975 IEEE International Solid-State Circuits Conference, Digest of Technical Papers, pages 168-169. Peltier states that either titanium, tungsten or titanium-tungsten alloy satisfy this requirement. However, these contacts have the shortcoming which we have discussed hereinbefore.